Frustrated total internal reflection (FTIR), where a second refractive material is introduced into a beam to change the direction of that beam, is a known technique for carrying out optical switching.
For example, U.S. Pat. No. 5,444,801, issued to Laughlin on Aug. 22, 1995, entitled “Apparatus for Switching Optical Signals and Method of Operation” is directed to an FTIR switch having a first switch plate that encodes a collimated beam in a shallow angle in first plane that is projected onto a second orthogonal switch plate that encodes a second orthogonal shallow angle on the collimated beam and is projected through a single lens onto a focal plane to a plurality of fibers. Unfortunately, this FTIR switch is limited by the number of fibers that can be placed at the focal plane of the lens with an acceptable lens blur (and concomitant coupling loss) and the ability to precisely position each fiber to a submicron level at the focal plane. For this reason, this FTIR switch is limited to 1×N switching and to the number of fibers that can be accommodated at the focal plane. Thus this FTIR switch requires that the number of switch plates equal log2 (N outputs).
Another example is U.S. Pat. No. 6,236,778, also issued to Laughlin on Aug. 22, 1995, entitled “Apparatus for Switching Optical Signals and Method of Operation” and directed to an N×M FTIR switch matrix (N and M each representing a bus). The input bus has N inputs, and the output bus has M inputs. The FTIR switch matrix requires that the input bus and output bus be orthogonal to each other and in contact at interface nodes thereof. Both the input bus and the output bus are individual refractive elements. An input beam is reflected at input nodes down the input bus and switched at one of the interface nodes, by both the input bus and the output bus, and then reflected down the output bus at reflection nodes thereof. Unfortunately, the FTIR switch matrix requires M plus N individual buses (refractive elements) and two frustrating elements for every interface node. Consequently, the FTIR switch matrix requires not only that first and second frustrating elements be precisely aligned, but also that each of the M plus N buses must be precisely aligned with each other and in intimate contact (within a few angstroms) of each other.
With a growing emphasis on fiber networks, there is a growing requirement to employ N×M switching in those networks. One method commonly used today to facilitate an N×M switch is to use two arrays of 1×N switches. N inputs and M outputs require (M+N) 1×N switches. For example, eight 1×4 switches are required to implement a 4×4 switch. The eight 1×4 switches have a total of 5×8=40 input/output ports and 8×4=32 switch elements and corresponding drivers. Each of these input/output ports and switch elements and corresponding drivers are expensive both in terms of material and labor to fabricate, assemble and align precisely.